A cellular telephone system provides radio communication between a stationary base system and remote units, e.g., mobile radio-telephones installed in automobiles. The base system typically includes a switching system, a network of geographically separated basestations, and other equipment. Each basestation defines a particular cell of the cellular system, and has at least one transceiver with the capability of calling to and receiving calls from remote units in the corresponding cell. Such a cellular telephone system is described in the Bell System Technical Journal, January 1979, entitled, "The Cellular Concept," page 15 et seq.
Cellular telephone systems are subject typically to governmental regulations and approvals, and must comply with standards, such as, for example, those set forth for the United States of America in EIA RS-553 by Electronic Industries Association, Washington, D.C., U.S.A.
A known cellular telephone system allocates to each basestation a plurality of radio channels to carry voice signals (called "voice channels"), and at least one separate signalling or control radio channel. In turn, the basestation assigns the allocated voice channels to remote units for use during voice telephone calls; the assignments of the voice channels being made in response to requests from the remote units for cellular service for the calls. This preliminary procedure of requesting and assigning a voice channel occurs over the control channel, and can be referred to as a "hand-shake" transaction. Hand-shake transactions occupy valuable time on the control channel.
Furthermore, because of the nature of cellular speech traffic, substantial voice channel capacity is sometimes idle, e.g., between telephone calls. This is even more pronounced during certain periods of the day, and during week-ends and holidays.
It has been proposed to provide data communication service in addition to voice service over cellular telephone systems. Two general alternatives exist in the prior art. In one approach, the cellular telephone system sends data as well as speech information over the voice channels, thereby purportedly improving radio channel utilization. One such system is described in U.S. Patent No. 4,887,265. Sharing channels with data in accordance with that approach, however, degrades voice service insofar as the data competes with voice traffic for channel utilization, and degrades overall system performance in that control channels are used to carry both data and voice communication requests.
A second approach avoids interference with voice services by establishing a separate cellular data system operating over data-only channels in frequency bands distinct from those of the voice system. One such system is described in U.S. Pat. No. 4,914,651. This approach, however, does not provide for efficient use of the frequency spectrum, and might be subject to new governmental regulation and approvals, and the promulgation of new standards for the cellular data system.